Adaptive periodic waveform controller

ABSTRACT

A repeating setpoint generator module selectively varies a setpoint for an output parameter according to a predetermined pattern that repeats during successive time intervals. A closed-loop module, during a first one of the time intervals, generates N closed-loop values based on N differences between (i) N values of the setpoint at N times during the first one of the time intervals and (ii) N measurements of the output parameter at the N times during the first one of the time intervals, respectively. An adjusting module, during the first one of the time intervals, generates N adjustment values based on N differences between (i) N values of the setpoint at the N times during a second one of the time intervals and (ii) N measurements of the output parameter at the N times during the second one of the time intervals, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Divisional application Ser.No. 16/005,761, filed on Jun. 12, 2018, which claims the benefit of U.S.application Ser. No. 14/953,917, filed on Nov. 30, 2015, which claimsthe benefit of U.S. Provisional Application No. 62/087,290, filed onDec. 4, 2014. The entire disclosures of the above applications areincorporated herein by reference.

FIELD

The present disclosure relates to plasma chambers and to radio frequency(RF) generation systems and methods and more particularly to RFgenerators.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

A radio frequency (RF) generator receives alternating current (AC) inputpower and generates an RF output. The RF output may be applied to, forexample, a plasma electrode of a plasma chamber. Plasma chambers may beused in thin film manufacturing systems and other types of systems.

In some circumstances, a plasma chamber may include a plurality ofplasma electrodes. For example only, more than one plasma electrode maybe implemented where a surface area being treated is larger than an areathat a single plasma electrode may be capable of servicing.

Accordingly, multiple RF generators may be employed in somecircumstances. Each of the RF generators generates an RF output andapplies the RF output to one of the plasma electrodes. The RF generatorsmay be electrically connected in an effort to generate identical RFoutputs.

SUMMARY

In a feature, a power output generation system is disclosed. A repeatingsetpoint generator module selectively varies a setpoint for an outputparameter according to a predetermined pattern that repeats duringsuccessive time intervals. A closed-loop module, during a first one ofthe time intervals, generates N closed-loop values based on Ndifferences between (i) N values of the setpoint at N times during thefirst one of the time intervals and (ii) N measurements of the outputparameter at the N times during the first one of the time intervals,respectively. An adjusting module, during the first one of the timeintervals, generates N adjustment values based on N differences between(i) N values of the setpoint at the N times during a second one of thetime intervals and (ii) N measurements of the output parameter at the Ntimes during the second one of the time intervals, respectively. Thesecond one of the time intervals is the time interval immediatelypreceding the first one of the time intervals. A power amplifier appliesan output power to a load. A mixer module generates N output valuesbased on the N closed-loop values and the N adjustment values,respectively, and controls power input to the power amplifier based onthe N output values.

In further features, the N times are equally spaced.

In further features, the N times are not equally spaced.

In further features, the closed-loop module generates the N closed-loopvalues using proportional-integral (PI) control.

In further features, the adjusting module generates the N adjustmentvalues using proportional-integral (PI) control.

In further features, the mixer module generates the N output valuesfurther based on a mixing ratio, and the mixer module selectively variesthe mixing ratio.

In further features, a frequency control module selectively adjusts afundamental frequency of the power amplifier.

In further features, the frequency control module selectively adjuststhe fundamental frequency of the power amplifier based on a reflectedpower.

In further features, the frequency control module selectively adjuststhe fundamental frequency of the power amplifier based on a reflectioncoefficient.

In further features, the power amplifier applies the output to a plasmaelectrode.

In further features, a driver control module that determines adistortion of the output and selectively adjusts a fundamental frequencyof the power amplifier based on the distortion.

In further features, the driver control module determines a firstfrequency adjustment based on the distortion and at least one previousamount of distortion of the output, determines a second frequencyadjustment based on at least one previous amount of distortion of theoutput, and that sets the fundamental frequency of the power amplifierbased on a previous switching frequency of the power amplifier, thefirst frequency adjustment, and the second frequency adjustment.

In further features, the driver control module determines the secondfrequency adjustment based on at least one previous value of the secondfrequency adjustment.

In a feature, a method of generating a power output is disclosed. Themethod includes: selectively varying a setpoint for an output parameteraccording to a predetermined pattern that repeats during successive timeintervals; during a first one of the time intervals, generating Nclosed-loop values based on N differences between (i) N values of thesetpoint at N times during the first one of the time intervals and (ii)N measurements of the output parameter at the N times during the firstone of the time intervals, respectively; during the first one of thetime intervals, generating N adjustment values based on N differencesbetween (i) N values of the setpoint at the N times during a second oneof the time intervals and (ii) N measurements of the output parameter atthe N times during the second one of the time intervals, respectively,wherein the second one of the time intervals is the time intervalimmediately preceding the first one of the time intervals; applying,using a power amplifier, an output power to a load; generating N outputvalues based on the N closed-loop values and the N adjustment values,respectively; and controlling power input to the power amplifier basedon the N output values.

In further features, the N times are equally spaced.

In further features, the N times are not equally spaced.

In further features, generating the N closed-loop values comprisesgenerating the N closed-loop values using proportional-integral (PI)control.

In further features, generating the N adjustment values comprisesgenerating the N adjustment values using proportional-integral (PI)control.

In further features, the method further includes: generating the Noutput values further based on a mixing ratio; and selectively varyingthe mixing ratio.

In further features, the method further includes selectively adjusting afundamental frequency of the power amplifier.

In further features, the method further includes selectively adjustingthe fundamental frequency of the power amplifier based on a reflectedpower.

In further features, the method further includes selectively adjustingthe fundamental frequency based on a reflection coefficient.

In further features, the method further includes applying, using thepower amplifier, the output to a plasma electrode.

In further features, the method further includes: determining adistortion of the output; and selectively adjusting a fundamentalfrequency of the power amplifier based on the distortion.

In further features, the method further includes: determining a firstfrequency adjustment based on the distortion and at least one previousamount of distortion of the output; determining a second frequencyadjustment based on at least one previous amount of distortion of theoutput; and setting the switching frequency of the power amplifier basedon a previous fundamental frequency of the power amplifier, the firstfrequency adjustment, and the second frequency adjustment.

In further features, the method further includes determining the secondfrequency adjustment based on at least one previous value of the secondfrequency adjustment.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example radio frequency (RF)plasma chamber control system;

FIG. 2 is a functional block diagram of an example portion of the RFplasma chamber control system;

FIG. 3 is a functional block diagram of an example feedback controlsystem;

FIG. 4 is a functional block diagram of an example RF generator system;

FIG. 5 includes graphs of example patterns that can be repeated withincycles/periods;

FIG. 6 includes a functional block diagram of an example closed-loopcontrol module of an RF generator system;

FIG. 7 includes a functional block diagram of an example adjustingmodule;

FIGS. 8-13 include graphs of setpoints and measurements versus time;

FIG. 14 includes a flowchart depicting an example method of controllingRF output;

FIG. 15 is a functional block diagram of an example RF generator system;and

FIG. 16 is a functional block diagram of an example driver controlmodule.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

Referring now to FIG. 1, a functional block diagram of an example radiofrequency (RF) plasma chamber control system is presented. A radiofrequency (RF) generator module 104 receives alternating current (AC)input power and generates an RF output using the AC input power. The RFoutput is applied to a plasma electrode 108 of a plasma chamber 112. Inother types of systems, the RF output may be used differently. Theplasma electrode 108 may be used, for example, in thin film deposition,thin film etching, and other types of systems.

An output control module 116 receives a power setpoint (P Set) for theRF output generated by the RF generator module 104 and that is deliveredto the plasma electrode 108. The power setpoint may be provided, forexample, via an external interface 120 or another suitable source. Theexternal interface 120 may provide the power setpoint to the outputcontrol module 116, for example, based on a diagnostic or user inputprovided via a universal standard (US) RS-232 connection, via anEthernet connection, via a fieldbus connection (e.g., Profibus,DeviceNet, Ethercat) via a wireless connection, or via a front panelinterface. The setpoint may also be a voltage or current setpoint,depending on the plasma requirements.

An RF sensor 124 measures one or more parameters of the RF output andgenerates one or more sensor signals based on the measured parameter(s).For example only, the RF sensor 124 may include a voltage-current (VI)sensor, an RF probe, a directional coupler, a gamma sensor, aphase-magnitude sensor, or another suitable type of RF sensor.

A measurement control module 128 samples the sensor signal(s) at apredetermined sampling frequency. In various embodiments, themeasurement control module 128 converts the (analog) samples intocorresponding digital values. The measurement control module 128 alsoapplies one or more signal processing functions to the digital values toproduce processed values. The output control module 116 controls the RFgenerator module 104 to achieve the power setpoint. In variousembodiments, a matching network module 132 may be included that providesmatching. While the RF sensor 124 is shown as being upstream of thematching network module 132, in various embodiments, the RF sensor 124may be located between the matching network module 132 and the load.

Referring now to FIG. 2, a functional block diagram including an exampleportion of the RF plasma chamber control system is presented. The outputcontrol module 116 may generate a rail voltage setpoint (Rail Set) and adriver control setpoint (Driver Set) based on the power setpoint. Basedon the rail voltage setpoint, a power supply module 304 generates a railvoltage from the AC input power. The power supply module 304 applies therail voltage to a RF power module 308. The RF power module 308 includes,for example, a driver module and a power amplifier. In variousimplementations, the output control module 116 may generate multiplephase-shifted driver signals for an outphasing amplifier topology.

A driver control module 312 drives the RF power module 308 based on thedriver control setpoint. The driver control setpoint may indicate atarget duty cycle (i.e., a percentage of ON time for each predeterminedperiod). A filter 316 may be implemented to filter the harmonic outputof the RF power module 308 (e.g., the power amplifier) before the RFoutput is applied to the plasma electrode 108. Outputs of one or moreactuators of the RF system (e.g., power supply module 304, the drivercontrol module 312) may be adjusted based on one or more parameters ofthe RF output measured by the RF sensor 124.

Referring now to FIG. 3, a functional block diagram of an examplefeedback control system for an actuator (e.g., the plasma electrode 108)is presented. The feedback actuator control system of FIG. 3 could beused to generate, for example, a pulsed RF signal output, an envelopefor a control or drive signal, or another suitable RF output. A pulsedRF signal output may refer to an output having repeating patternsincluding, but not limited to, equally spaced defined or arbitraryshaped patterns.

In a digital control system, which may also be referred to as a discretetime control system, the required closed-loop bandwidth of a controllerable to produce a suitable pulsed RF envelope output would need to be atleast two orders of magnitude greater than the period between the (sameportions) of the cycles. Additionally, the group delays of sensors andactuators would need to be on the order of the controller sampling time.A suitable control system may therefore be complex and expensive.

In FIG. 3, a control module 350 includes an error module 354, aproportional (P) module 358, an integral (I) module 362, a summer module366, and a clamping module 370. The error module 354 determines an errorbased on a difference between a setpoint for a parameter (e.g., thepower setpoint) and a measured value of that parameter.

The proportional module 358 determines a P term value based on aproportional gain and the error value. The integral module 362determines an I term value based on the error and an integral gain. Thesummer module 366 sums the P term value and the I term value todetermine an output. The clamping module 370 may limit the output towithin a predetermined range. The actuator (e.g., the power supplymodule, the driver amplitude, outphasing drive, etc.) is controlledbased on the output. A control system including this control module,however, may be complex and expensive, as described above.

Another way to control the output based on the setpoint is described incommonly assigned U.S. Pat. No. 6,700,092 (“Vona”), the entiredisclosure of which is incorporated herein. In Vona, a “holdoff time” ora delay period is used to jump in a discontinuous fashion from one pulsestate to another. The controller is frozen during the holdoff time toallow the pulse amplitude to settle at the new value beforetransitioning to closed loop operation. In this configuration, a slowercontrol loop bandwidth can be used than that described above inconjunction with FIG. 3. However, the use of the holdoff time may affectovershoot, rise time, and other responses.

The responses of Vona can be improved, for example, by ramping theoutput in open-loop towards the value where the amplitude will settleduring the holdoff time. Such a configuration is described in commonlyassigned U.S. Pat. No. 8,736,377 (“Rughoonundon”), the entire disclosureof which is incorporated herein. The ramping can be performed formultiple outputs/actuators, such as amplitude, frequency, etc.Rughoonundon provides better responses for rectangular pulses.

FIG. 4 includes a functional block diagram of an example RF controlsystem including an RF generator module 404, an RF power amplifier 408,and one or more sensors 412. The RF generator module 404 controls thepower amplifier 408 to regulate RF output from the RF power amplifier408, such as to a plasma electrode or another RF device. The RF poweramplifier 408 may be a component of the RF power module 308 of FIG. 2.

A repeating setpoint generator module 416 generates forward power (PFwd)setpoints according to a repeating pattern within cycles or periods. Afrequency control module 420 controls a fundamental RF frequency of thedriver control module 312. The frequency control module 420 may vary thefrequency, for example, to improve complex impedance matching and,therefore, decrease reflected power and a reflection coefficient. Anenvelope may define one or both (upper and lower) bounds of the outputsignal within a cycle/period.

The repeating pattern may be, for example, stored in memory. FIG. 5includes three examples of patterns that may be repeated, however, otherpatterns may be used. In various implementations, the pattern used maybe a non-standard, periodic pattern. Standard periodic patterns include,for example, sine waves, cosine waves, periodic pulses, triangularwaves, etc. The frequency corresponds to the time period within therepeating pattern is performed once. The repeating setpoint generatormodule 416 varies the forward power setpoints according to one cycle ofthe pattern within each time period/cycle. While the example of forwardpower setpoints and forward power measurements will be discussed, thepresent application is also applicable to other RF setpoints and thecorresponding measurements.

A closed-loop control module 424 generates a closed-loop output at agiven time based on the forward power amplitude setpoint (sample) forthat time and forward power amplitude (sample) measured by the sensor412 for that time. More specifically, the closed-loop control module 424generates the closed-loop output to adjust the forward power amplitudetoward the forward power amplitude setpoint. A functional block diagramof an example of the closed-loop control module 424 is shown in FIG. 6.As stated above, while the example of forward power amplitude setpointsand forward power amplitude measurements will be discussed, the presentapplication is also applicable to other RF setpoints and thecorresponding measurements, such as voltage and/or current amplitude.

Referring now to FIG. 6, the closed-loop control module 424 includes anerror module 504, a proportional (P) module 508, an integral (I) module512, and a summer module 516. The error module 504 determines a forwardpower error based on a difference between the forward power setpoint ata time and the forward power measured using the sensor 412 at that time.

The proportional module 508 determines a proportional term (value) basedon a predetermined proportional gain and the forward power error. Theintegral module 512 determines an integral term (value) based on apredetermined integral gain and the forward power error. The integralmodule 512 may limit (i.e., clamp) the integral term to within apredetermined range. The summer module 516 sums the P term and the Iterm to generate the closed-loop output. While the example of a PIclosed-loop controller is shown and discussed, a P (proportional)closed-loop controller, a PID (proportional-integral-derivative)closed-loop controller, or another suitable type of closed-loopcontroller may be used.

Referring back to FIG. 4, the RF generator module 404 also includes atriggering module 428, a setpoint storage module 432, and a measurementstorage module 436. The triggering module 428 generates a trigger signalN times during each cycle. N is an integer greater than 1. In oneexample, the triggering module 428 may generate the trigger signal 86times during each cycle.

The triggering module 428 may generate the trigger signal inpredetermined (time) intervals, or the interval between times when thetrigger signal is generated may vary. In the case of different intervalsbetween trigger signals, the triggering module 428 may, for example,generate the trigger signal more frequently near and when the forwardpower setpoint (and therefore the repeating pattern) changes. When theforward power setpoint is more steady, the triggering module 428 maygenerate the trigger signal less frequently. The triggering module 428generates the trigger signal N number of times during each cycle andgenerates the trigger signal at the same N times during each cyclerelative to the cycles' respective start and end. The closed-loopcontrol module 424 may also update the closed-loop output each time thatthe trigger signal is generated.

The setpoint storage module 432 stores the present value of the forwardpower setpoint each time that the trigger signal is generated. When acycle is completed, the setpoint storage module 432 has therefore storedN values of the forward power setpoint at the N times within that cycle.The measurement storage module 436 stores the present value of theforward power each time that the trigger signal is generated. When acycle is complete, the measurement storage module 436 has thereforestored N values of the forward power at the N times within that cycle.

Each time that the trigger signal is generated at one of the N times,the setpoint storage module 432 and the measurement storage module 436output the forward power setpoint and the forward power, respectively,stored for that one of the N times during the last cycle. The forwardpower setpoint from that time during the last cycle will be referred toas the previous forward power setpoint. The forward power measured atthat time during the last cycle will be referred to as the previousforward power. In various implementations, the previous forward powercan be a composite value determined based on multiple previous cycles.Such a composite value can be determined in various ways, such as usingan Infinite Impose Response (IIR) filter. Use of such a composite valuemay reduce the effects of noise and plasma transient phenomena.

An adjusting module 440 generates an output adjustment at a given timebased on the previous forward power setpoint for that time and theprevious forward power measured by the sensor 412 for that time duringthe last cycle. A functional block diagram of an example of theadjusting module 440 is shown in FIG. 7.

Referring now to FIG. 7, the adjusting module 440 includes an errormodule 604, a proportional (P) module 608, an integral (I) module 612,and a summer module 616. The error module 604 determines a previouserror based on a difference between the previous forward power setpointat a time and the previous forward power at that time.

The proportional module 608 determines a proportional term (value) basedon a predetermined proportional gain and the previous error. Theintegral module 512 determines an integral term (value) based on apredetermined integral gain and the previous error. The integral module512 may limit (i.e., clamp) the integral term to within a predeterminedrange. The summer module 516 sums the P term and the I term to generatethe output adjustment. The output adjustment at a time thereforereflects the closed-loop output at that time during the previous cycle.

While the example of a PI closed-loop controller is shown and discussed,a P (proportional) closed-loop controller, a PID(proportional-integral-derivative) closed-loop controller, or anothersuitable type of closed-loop controller may be used. Also, while storageof the previous forward power setpoint and the previous forward power isshown and discussed, the values of the error (determined by the errormodule 504) determined for the N times during a cycle may be stored andused for those N times, respectively, during the next cycle.

Referring back to FIG. 4, a mixer module 444 mixes the closed-loopoutput with the output adjustment to produce a final RF output. Themixer module 444 may mix the closed-loop output and the outputadjustment, for example, based on a mixing ratio. The mixing ratio maybe a predetermined value or may vary. For example, the mixer module 444may vary the mixing ratio depending on desired behavior, such as loadtransient sensitivity or other rules, or may be set by another (e.g.,higher level) controller. The mixing ratio may correspond to gainsapplied to the closed-loop output and the output adjustment such that,when the gain applied values are summed, result in the final RF output.

A clamping module 448 may limit (i.e., clamp) the final RF output towithin the predetermined range. An actuator of the RF generator, such asthe power amplifier/driver 408, is operated based on the final RF outputto produce an RF output. The driver control module 312 controls afundamental operating frequency of the power amplifier/driver 408. Thefundamental operating frequency may also be referred to as the carrierfrequency. The RF output may be applied, for example, to the plasmaelectrode 108 or another RF device.

Use of the adjusting module 440 improves response characteristics. Forexample, the adjusting module 440 may enable the forward power to moreclosely follow the forward power setpoint, may do so sooner (e.g., in alesser number of cycles), and with less over and/or undershoot than, forexample, an RF generator module implementing the system of FIG. 3. Whilethe example of RF envelope outputs and setpoints has been shown anddiscussed, the present application is also applicable to other non-RFoutputs, such as direct current (DC) outputs (involving repeating DCsetpoints), and alternating current (AC) outputs (involving repeating ACsetpoints). This approach may be increasingly effective in systemsincluding one or more component modules having nonlinear transfercharacteristics. In such systems, it may be difficult to useconventional linear control techniques when one or more subsystemsexhibit gain expansion, gain compression, or clipping, such as thatwhich may happen with RF power amplifiers. Plasma loads may also exhibitnonlinear behavior, such as load impedance that varies with appliedpower.

FIG. 8 includes an example graph of setpoints and measurements versustime during a first cycle for a setpoint set according to a repeating,predetermined shape. In the example of FIG. 8, the shape is arectangular pulse or square wave. During the first cycle, no setpointsor measurements have been stored from one or more previous cycles. Thus,the output is controlled using only closed-loop feedback based on thedifferences between the setpoints and the measurements during thatcycle. Differences between the measured and desired waveforms may beattributable to nonlinearities present in the power amplifiersubsystems. After the first cycle, however, the previous setpoints andmeasurements are also used to control the output, and the measurementstherefore more closely track the setpoints (e.g., see FIG. 9, cycles 1,2, 10, and 100.

FIGS. 9-13 are example graphs illustrating this feature and includesetpoints having various different repeating shapes. As shown in FIGS.9-13, the measurements more closely track the setpoints during latercycles. From FIGS. 9-13, it can be seen that the control systemdescribed herein can be used to generate sinusoidal, square, orarbitrary shaped waveforms. The generated waveforms can define a primarysignal, or the generated waveforms may define an envelope signal withinwhich a drive signal operates. The drive signal and the envelope signalmay be continuous waves or pulsed signals.

FIG. 14 is a flowchart depicting an example method of controlling anoutput. Control begins with 704 where a counter value (I) is set to 1.At 708, it is determined whether the present cycle is a first cycle, forexample, after a different repeating pattern was selected or after theunit is turned ON. If 708 is true, control continues with 712. If 708 isfalse, control transfers to 730, which is discussed further below.

At 712, the trigger signal is monitored, and a determination is made asto whether the trigger signal has been generated. When the triggersignal is generated, control continues with 716. When the trigger signalis not generated, control may remain at 712. At 716, the setpointstorage module 432 stores the I-th setpoint (e.g., forward powersetpoint), and the measurement storage module 436 stores the I-thmeasured value (e.g., measured forward power). The closed-loop controlmodule 424 determines the closed-loop output based on a differencebetween the I-th setpoint and the I-th measured value at 720. At 722,the mixer module 444 sets the output equal to the closed-loop output. Anactuator, such as the power amplifier/driver 408, is controlled based onthe output.

At 724, a determination is made as to whether the counter value (I) isless than a predetermined number (N). The predetermined numbercorresponds to the number of instances that the trigger signal isgenerated during each cycle. If 724 is true, the counter value (I) isincremented (e.g., I=I+1) at 728, and control returns to 712. If 724 isfalse, control returns to 704 to reset the counter value (I) to 1.

At 730, after the first cycle is complete, the trigger signal ismonitored, and a determination is made as to whether the trigger signalis generated. When the trigger signal is generated, control continueswith 732. When the trigger signal is not generated, control may remainat 730. At 732, the setpoint storage module 432 stores the I-th setpoint(e.g., forward power setpoint), and the measurement storage module 436stores the I-th measured value (e.g., measured forward power). Theclosed-loop control module 424 determines the closed-loop output basedon a difference between the I-th setpoint and the I-th measured value at736.

At 740, the adjusting module 440 obtains the I-th setpoint from the lastcycle and the I-th measurement from the last cycle. The adjusting module440 generates the output adjustment at 744 based on a difference betweenthe I-th setpoint from the last cycle and the I-th measurement from thelast cycle. At 748, the mixer module 444 mixes the closed-loop output(determined at 736) with the output adjustment (determined at 744) toproduce the output. As stated above, a actuator, such as the poweramplifier/driver 408, is controlled based on the output.

At 752, a determination is made as to whether the counter value (I) isless than the predetermined number (N). The predetermined numbercorresponds to the number of instances that the trigger signal isgenerated during each cycle. If 752 is true, the counter value (I) isincremented (e.g., I=I+1) at 756, and control returns to 730. If 756 isfalse, control returns to 704 to reset the counter value (I) to 1.

FIG. 15 is a functional block diagram of an RF generation system. Inaddition to the control provided by the RF generator module 404, thedriver control module 312 may control the fundamental RF operatingfrequency of the power amplifier/driver 408 based on one or moreparameters measured by the sensor(s) 412. For example, the frequency canbe adjusted to improve impedance matching of the RF power module 308 tothe plasma load.

FIG. 16 is a functional block diagram of an example implementation ofthe driver control module 312. A distortion module 804 determines anamount of distortion in the RF output based on one or more parametersmeasured by the sensor(s) 412. The amount of distortion may correspondto an amount of reflected power and may be indicated, for example, by areflection coefficient or reverse power.

First and second frequency adjustment modules 808 and 812 generate firstand second frequency adjustments in an effort to minimize the distortionand, therefore, minimize reflected power. The first frequency adjustmentmodule 808 generates the first frequency adjustment based on a presentamount of distortion, one or more previous amounts of distortion fromprevious times, respectively, and one or more predetermined gain values.Examples of first frequency adjustments are described in commonlyassigned U.S. Pat. Nos. 8,576,013, and 6,020,794, both of whichincorporated herein in their entirety. The second frequency adjustmentmodule 808 generates the second frequency adjustment based on one ormore previous amounts of distortion from previous times, respectively,one or more previous values of the second frequency adjustment, and oneor more predetermined gain values.

A mixer module 812 determines the fundamental operating frequency of thepower amplifier/driver 408 based on a previous fundamental operatingfrequency of the power amplifier/driver 408, the first frequencyadjustment, and the second frequency adjustment. For example, the mixermodule 812 may set the fundamental operating frequency of the poweramplifier/driver 408 to the previous fundamental operating frequencyminus the first and second frequency adjustments. A delay module 820provides the previous fundamental operating frequency after it has beenstored for a predetermined period (e.g., one sampling period). The mixermodule 812 may selectively vary gain values applied to the first andsecond frequency adjustments before the subtraction in variousimplementations.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules) are described using various terms, including“connected,” “engaged,” “interfaced,” and “coupled.” Unless explicitlydescribed as being “direct,” when a relationship between first andsecond elements is described in the above disclosure, that relationshipencompasses a direct relationship where no other intervening elementsare present between the first and second elements, and also an indirectrelationship where one or more intervening elements are present (eitherspatially or functionally) between the first and second elements. Asused herein, the phrase at least one of A, B, and C should be construedto mean a logical (A OR B OR C), using a non-exclusive logical OR, andshould not be construed to mean “at least one of A, at least one of B,and at least one of C.”

In this application, including the definitions below, the term ‘module’or the term ‘controller’ may be replaced with the term ‘circuit.’ Theterm ‘module’ may refer to, be part of, or include processor hardware(shared, dedicated, or group) that executes code and memory hardware(shared, dedicated, or group) that stores code executed by the processorhardware.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. Shared processor hardware encompasses asingle microprocessor that executes some or all code from multiplemodules. Group processor hardware encompasses a microprocessor that, incombination with additional microprocessors, executes some or all codefrom one or more modules. References to multiple microprocessorsencompass multiple microprocessors on discrete dies, multiplemicroprocessors on a single die, multiple cores of a singlemicroprocessor, multiple threads of a single microprocessor, or acombination of the above.

Shared memory hardware encompasses a single memory device that storessome or all code from multiple modules. Group memory hardwareencompasses a memory device that, in combination with other memorydevices, stores some or all code from one or more modules.

The term memory hardware is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium is therefore considered tangible and non-transitory. Non-limitingexamples of a non-transitory computer-readable medium are nonvolatilememory devices (such as a flash memory device, an erasable programmableread-only memory device, or a mask read-only memory device), volatilememory devices (such as a static random access memory device or adynamic random access memory device), magnetic storage media (such as ananalog or digital magnetic tape or a hard disk drive), and opticalstorage media (such as a CD, a DVD, or a Blu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks andflowchart elements described above serve as software specifications,which can be translated into the computer programs by the routine workof a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory computer-readable medium. Thecomputer programs may also include or rely on stored data. The computerprograms may encompass a basic input/output system (BIOS) that interactswith hardware of the special purpose computer, device drivers thatinteract with particular devices of the special purpose computer, one ormore operating systems, user applications, background services,background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective-C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for” or,in the case of a method claim, using the phrases “operation for” or“step for.”

What is claimed is:
 1. A power output generation system, comprising: asetpoint generator module that selectively varies a setpoint for anoutput parameter during successive time intervals; a closed-loop modulethat, during a first time interval, generates a closed-loop signal basedon the setpoint and a measurement of the output parameter during thefirst time interval, respectively; an adjusting module that, during thefirst time interval, generates an adjustment signal based on thesetpoint during a prior time interval and the output parameter duringthe prior time interval, respectively; and a power amplifier thatapplies an output to a load in accordance with the closed-loop signaland the adjustment signal.
 2. The power output generation system ofclaim 1 wherein the first time interval and prior time interval areequally spaced.
 3. The power output generation system of claim 1 whereinthe first time interval and prior time interval are not equally spaced.4. The power output generation system of claim 1 wherein the closed-loopmodule generates the closed-loop signal using proportional-integral (PI)control.
 5. The power output generation system of claim 1 wherein theadjusting module generates the adjustment signal usingproportional-integral (PI) control.
 6. The power output generationsystem of claim 1 further comprising a mixer module that generates anoutput signal based on the closed-loop signal and the adjusting signal,respectively, and that controls power input to the power amplifier basedon the output signal, the mixer module generates the output signalfurther based on a mixing ratio, and wherein the mixer moduleselectively varies the mixing ratio.
 7. The power output generationsystem of claim 1 further comprising a frequency control module thatselectively adjusts a fundamental frequency of the power amplifier. 8.The power output generation system of claim 7 wherein the frequencycontrol module selectively adjusts the frequency of the power amplifierbased on a reflected power.
 9. The power output generation system ofclaim 7 wherein the frequency control module selectively adjusts thefrequency of the power amplifier based on a reflection coefficient. 10.The power output generation system of claim 1 wherein the poweramplifier applies the output to a plasma electrode.
 11. The power outputgeneration system of claim 1 further comprising a driver control modulethat determines a distortion of the output and selectively adjusts afrequency of the power amplifier based on the distortion.
 12. The poweroutput generation system of claim 11 wherein the driver control moduledetermines a first frequency adjustment based on the distortion and atleast one previous amount of distortion of the output, determines asecond frequency adjustment based on at least one previous amount ofdistortion of an RF output, and that sets the frequency of the poweramplifier based on a previous frequency of the power amplifier, thefirst frequency adjustment, and the second frequency adjustment.
 13. Thepower output generation system of claim 12 wherein the driver controlmodule determines the second frequency adjustment based on at least oneprevious value of the second frequency adjustment.
 14. A power outputgeneration control system for controlling a power amplifier that appliesoutput power to a load, comprising: a repeating setpoint generatormodule that selectively varies a setpoint for an output parameteraccording to a predetermined pattern that repeats during successive timeintervals; an adjusting module that, during a first time interval,generates an adjustment signal based on the setpoint during a prior timeinterval and of the output parameter during the prior time interval,respectively; and a mixer module that generates an output signal basedon a closed-loop signal and the adjustment signal, respectively, andthat controls power input to the power amplifier based on the outputsignal.
 15. The power output generation control system of claim 14further comprising a closed-loop module that, during the first timeinterval, generates the closed-loop signal based on the setpoint and ameasurement of the output parameter during the first time interval,respectively.
 16. The power output generation control system of claim 15further comprising a power amplifier that applies the output power tothe load.
 17. The power output generation control system of claim 14further comprising a power amplifier that applies the output power tothe load.
 18. The power output generation control system of claim 14wherein the first time interval and prior time interval are equallyspaced.
 19. The power output generation control system of claim 14wherein the first time interval and prior time interval are not equallyspaced.
 20. The power output generation control system of claim 14wherein the adjusting module generates the adjustment signal using atleast one of proportional, integral, or derivative control.
 21. Thepower output generation control system of claim 14 wherein the mixermodule generates the output signal further based on a mixing ratio, andwherein the mixer module selectively varies the mixing ratio.
 22. Thepower output generation control system of claim 14 further comprising afrequency control module that selectively adjusts a fundamentalfrequency of the power amplifier.
 23. The power output generationcontrol system of claim 22 wherein the frequency control moduleselectively adjusts the frequency of the power amplifier based on one ofa reflected power or a reflection coefficient.